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<center><h3>Water in Chemical Equilibria:</h3></center>

<p>
In general diluted aqueous solutions are studied: water <nobr>(H<sub>2</sub>O)</nobr>
will be in excess and its activity may be considered to be constant,
and therefore set equal to one
<nobr>(log&nbsp;<a href="SP_Activity.htm">activity</a></nobr> <nobr>=&nbsp;0).</nobr>
</p>

<p>However, water <nobr>(H<sub>2</sub>O)</nobr> might be needed as a component if you wish
to model ionic medium effects, especially on systems where minerals precipitate
involving H<sub>2</sub>O, such as gypsum
<nobr>(CaSO<sub>4</sub>&#183;2H<sub>2</sub>O)</nobr>.

<p>Therefore it is recommended that
H<sub>2</sub>O is included in the reactions.</p>

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